1. Field of the Invention
The present invention relates to a dielectric ceramic and electronic parts using the same, and particularly, to the dielectric ceramic which is applied, for example, in a micro-stripline device, a monolithic IC, a polarizer and so on, and the electronic parts using the dielectric ceramic.
2. Description of the Prior Art
Conventionally, as a dielectric ceramic used in electronic parts, those having a uniform composition and a uniform dielectric constant distribution have been used.
For example, as a dielectric substrate used in a conventional micro-stripline device, there was the dielectric substrate having a uniform composition structure in which such material as alumina and fluororesin having a dielectric constant of 10 or so are used.
In such a dielectric substrate, by increasing the dielectric constant, the micro-stripline device or the substrate can be miniaturized. However, when the dielectric constant is increased, a width of stripline must also be narrowed in order to satisfy a characteristic impedance standard.
When considering miniaturization of the stripline device with the conventional dielectric substrate, under the condition of 1 mm substrate thickness and 50.OMEGA. characteristic impedance, a necessary line width of about 1.0 mm for the substrate of dielectric constant of 10. On the other hand, a necessary line width for the substrate of dielectric constant of 30 is about 0.2 mm. Accordingly, when miniaturizing by increasing the dielectric constant of the substrate, the line width becomes so narrow that it is difficult to contact to external circuits at input/output terminals.
Similarly, when the substrate having the uniform composition is used as the monolithic IC substrate, the line width formed on the substrate is determined by the characteristic impedance. Therefore, when the dielectric constant of the substrate is increased to reduce the line width, it is difficult to make contact to the external circuits.
In a satellite broadcasting system, as shown in FIGS. 25(A) and (B), a polarizer comprises a waveguide 1 into which a dielectric plate 2 having a dielectric constant of about 10 is inserted. In this dielectric plate 2 is that, the dielectric constant of the dielectric plate in an axial direction of the waveguide is changed continuously by forming V-shaped inclined portions 3 at its opposite ends. As such, by changing the dielectric constant of the dielectric plate, when an electric wave is incident to the polarizer or radiated from the polarizer, reflection of the electric wave at a border of the dielectric plate and air is prevented.
Also, this polarizer can be miniaturized by using a ceramics having a high dielectric constant for the dielectric plate. However, when the ceramic having the high dielectric constant is used, a difference of dielectric constant between air and the dielectric plate becomes larger, so that a propagation wave such as an interface wave is produced at the border between the air and the dielectric plate, which results in increasing a transmission loss.